Revolution switch



Dec. 22, 1959 FRANz-.JosEF voN BOMHARD 2,918,545

REVOLUTION SWITCH 2 Sheets-.Sheet 1 Filed Feb. 11, 1958 /N VEN I'Cl'` Fra/721705# van Bomba/'d 22, 1959 rumba-.JOSEF voN BOMHARD 2,918,545

REVOLUTION swITcH Filed Feb. l1, 1958 2 Sheets- Sheet 2 /N VEN raz? Fran z josef von 5cm/mrc( MGLJwM/m ATTOTLNESE,

United States Patent REVOLUTION SWITCH Franz-Josef von Bomhard, Schweinfurt (Main), Germany, assigner to Fichtel & Sachs A.G., Schweinfurt (Main), Germany This invention relates to a revolution switch and refers more particularly to a mercury switch actuated depending upon the number ofrevolutions of a rotary body and particularly suitablefor low speeds.

Revolution switches known in prior art are so constructed that the opening or the closing of la pair of contacts takes place at a predetermined number of revolutions of a rotary body through the use of centrifugal weights mostly connected with springs `and attached to mechanical transmission members.

Certain switching operations in the course of switching of automatically actuated couplings of motor-driven vehicles, require the use of very low speeds; by way of example, switches are required to prevent an increase 'in the number of revolutions of a motor during the actuation of the coupling while the vehicle is standing still, and to facilitate such increase at a comparatively slow vehicle speed of, say, kilometers per hour. If a revolution switch of the above-described known type is operated with the number of revolutions of the speedometer, the speed required for the switching will be approximately 200 r.p.m.; then in order to provide adequate contact pressure, the centrifugal bodies must have an unproportionately greatV weight, or, if the centrifugal bodies are of lighter weight, a very quickly operating transmission for the switch shaft is required. Both these requirements increase to a very great extent the costs of manufacture of switches of this type.. Furthermore, when speeds change rapidly, the driving elements of the switch shaft are subjected to substantially high stresses, with the result that various parts, such as the speedometer spirals, are liable to being damaged.

An object of the present invention is the provision of a revolution switch which avoids the above-described and other drawbacks of priory art constructions.

Other objects of the present invention will become apparent in the course Aof the following specification.

In accomplishing the objects of the present invention, it was found desirable to provide a switch wherein mercury is used as the contacting material, whereby the mercury changes its position within a closed rotary body depending upon the speed of rotation of the body. The mercury, depending upon its position, either establishes an electricalzconnection between two contact surfaces which are located within the rotary body and which are insulated one from the other, or it interrupts 'this connection.

The invention will appear more clearly from the following detailed description when taken in connection with the accompanying drawings showing, by way of example, preferred embodiments of the inventive idea.

In the drawings:

Figures 1, 2 and 3 tare longitudinal sections through a switch constructed in accordance with the principles of the present invention, and illustrate the mercury consttuting a pant of the switch in three different positions.

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Figure 4 is a similar section through a somewhat dierently constructed switch.

Figure 5 is a perspective view of a somewhat differently constructed rotary element constituting a part of the switch, a part of said rotary element being shown as being broken off.

Figures 1, 2 and 3 of the drawings illustrate 'an electrical switch which is operated automatically at a certain number of revolutions, and which is preferably used in conjunction with a motor vehicle. This switch includes a casing consisting of two parts 1 `and 2 and firmly mounted in the vehicle in any suitable manner. A shaft 3 is rotatably mounted within the casing 1, 2 and may have outwardly projecting ends which are 4suitable for attaching the shaft to the usual speedometer drive. The

shaft 3 must be mounted substantially vertically so as to avoid detrimental effects by the earth acceleration.

A casing consisting of two parts 4 and 5 is keyed upon the shaft 3, so that it is rotatable therewith, and is mounted withinthe outerfcasing 1, 2. The lower part 4 of the casing may consist'of an electrically conducting material. Upper casing portion 5, consisting essentially of an insulating material, is connected with the lower casing portion 4 in an air-tight manner. The upper casingportion 5 carries an electrically conducting contact surface member 6, which is conductively connected with a slip ring 7. However, the contact surface member 6 is insulated with respect to the shaft 3. The slip ring 7 receives electrical current from engagement with sliding contacts 8 which are insulated with respectto the casing portion 2 and which are vconnected with `a cable 9 for the transmission of Aelectrical current. The electrically conducting casing portion 4 is connected tothe same source of electrical Vcurrent through the shaft'3 and the casing 1, 2, which may be made of electrically conducting material.

A owing mercury mass10 is located within the inner casing 4, 5 and in the normal position of the switch is carried by the bottom casing portion 4.

The upper casing portion 5 has a rib extending toward the lower portion 4 so as to form Ian annular slot 11 extending between two concentrical chambers 11a and 11b provided within the casing- 4, 5. The' length of the slot 11 is of importance for the operation of the switch, as will be described in detail hereinafter. The lower casing portion 4 has an inclined surface 4a extending'toward and beyond the slot 11.

The operation of the switch is |as follows:

When the. shaft 3v is not rotated the mercury 10 is located in its lowermost position within the casing 4, 5l In this position, whichis shown -in Figure 1, the mercury 10 provides an electrical connection between the contact surface member 6 and the conducting casing portion 4, which constitutes the second contact surface member. Thus an electrical connection -is established through the source of electrical energy, the cable connection r9, the sliding contacts 8, the slip ring 7, the contact surface member 6, the mercury 10, the casing portion or contact surface member 4 and back to the source of electrical energy through the shaft 3. When the shaft 3 is rotated, the mercury 1'0`will assume substantially the form of a ring and, as shown in Figure 2, under the action of centrifugal forces will gradually move outwardly upon the inclined portion 4a of the member 4. It is apparent that the number of revolutions at which the mercury 10 will assume the position shown in Figure 2, depends upon the angle of the cone formed by the inclined surface 4a. However, in the position shown in Figure 2, the mercury 10 still provides a conducting connection between the contact surface members 6 and 4.

Practical experience has shown that revolution switches of this type require a cert-ain lag between the number of revolutions required for the switching on 'and the number of revolutions for the switching off, so as to eliminate a continuous, usually ickering switching when the vehicle moves for a longer time period within the range of the revolutions pertaining to the switching operations. The provision of the'two concentrical charnbers 11a and 11b separated by a slot 11 of predetermined length, is used in accordance with the present invention to -attain this result. Due to the high surface tension peculiar to mercury, the mass of mercury 10 Iwill ow through the slot 11 only when an additional force is provided. This is attained in that the mercury 10 will be forced through the slot 11 into the space 11b with a higher speed than the one which is set by the angle of the inclined surface 4a as the average speed. Furthermore, the mercury 10 will tlow from the chamber 11b back to the chamber 11a through the slot 11 at a lower speed than the .average speed. Thus the required lag is provided. The extent of the lag can be influenced by the length of the slot 11.

Figure 3 shows that when the device is rotated at higher speeds, the mercury passes through the slot 11 and will be located in its entirety in the chamber 11b. Then the electrical yconnection between the contact surface members 6 and 4 is interrupted.

Figure 4 illustrates a somewhat similar switch wherein, however, the electrical connection between the contact surface members 6a and 4 is interrupted when the switch stands still, or rotates at low speeds. Elements similar' to those shown in Figures 1 to 3 are designated by the same numerals. In this construction the contact surface member 6a projects into the chamber 11b, so that an electrical connection between the Contact surface members 6a and 4 is established at high speeds when the mercury 10 is located in the chamber 11b. In other respects the switch is essentially the same as the one previously described.

It is apparent that the switches shown in Figures l and 4 can be easily combined by the use of two concentrical slip rings insulated from each other and engaged by separate sliding contacts, so that one electrical circuit will be closed at standstill in the position shown in Figure 1, and another electrical circuit will be closed during rotation at higher speeds in the position shown in Figure 4.

It is apparent that only frctional engagement exists between the mercury 10 serving as the switching element which is actuated by centrifugal forces, and the casing 4, 5, which transmits the rotation. Consequently, there is a certain amount of slip when speeds change quickly. There is thus a certain time lag depending upon the angular acceleration between the time period when the casing 4, begins to rotate with the switching speed and the actual moment of switching. This slip has, on the one hand, the advantage that the mercury which constitutes a substantial proportion of the rotating masses, will not follow very quick speed changes which can take place, for example, when the drive does not operate uniformly, or when vibrations take place, so that the torque peaks for the drive are considerably reduced; on the other hand, the time lag can be detrimental in certain instances, depending upon the intended use of the switch.

This time lag can be diminished to a substantial extent,

4 y for example, through the use of special blade-like elements for accelerating the movement of mercury within the inner chamber 11a. Similar elements may be provided for retarding the movement of mercury in the outer chamber 11b. Obviously such members may be provided in both chambers.

Figure 5 illustrates a casing portion 5a having an annular chamber, the inner surface 12 of which is substantially star-shaped. Thus the surface 12 forms blades or paddles which facilitate the return tlow of the mercury when the speed of rotation of the casing portion 5a is diminished, with the result that the closing of the electrical circuit is thereby speeded up.

In order to avoid the oxidation of the mercury mass 10, or of the Contact surface members, the inner chamber of the rotary casing can be evacuated in the usual manner, or it can be lled with a suitable gas, such as nitrogen.

It is apparent that other variations and modifications may be made within the scope of the present invention. All such variations and modifications are to be included within the scope of the present invention.

What is claimed is:

A revolution switch, comprising a shaft, a rotary casing carried by said shaft and having two opposed contact surface members, means separating the interior of said casing into two concentrical chambers with an annular slot interconnecting said chambers, an inclined surface of constant slope throughout its length adjacent said slot, and an insulating portion carrying one of said contact surface members at a radial distance from said shaft and opposite the other one of said contact surface members, mercury within said casing, said mercury being movable through said slot and along said inclined surface to one position within one of said chambers and to another position within the other one of said chambers, said two contact surface members being conductively interconnected by said mercury in one of said positions, the conducting connection between the two contact surface members being interrupted when said mercury is in the other position, an accelerated rotation of said casing causing a centrifugal flow of said mercury along said inclined bottom portion to one of said two positions, said mercury being thrust through said slot in one direction by an addi tionally increased centrifugal force corresponding to a higher than average speed and said mercury being moved through said slot in the opposite direction by an additionally diminished centrifugal force corresponding to a lower than average speed, one of said concentrical chambers having uniformly spaced radially extending blades dividing the chamber into a plurality of communicating compartments.

References Cited in the le of this patent UNITED STATES PATENTS 1,498,113 Olds June 17, 1924 1,588,459 Kilgour June 15, 1926 1,785,705 Taylor Dec. 16, 1930 1,983,502 Vaughan Dec. 4, 1934 2,164,991 Ingres Iuly 4, 1939 2,205,375 Dyer Iune 18, 1940 2,291,237 Kilgour July 28, 1942 2,438,067 Luhn Mar. 16, 1948 

